JP 09-170554 A discloses an acoustic outlet piece for compressor, which includes attenuators symmetrically provided around a path having a uniform diameter.
In the acoustic outlet piece, the attenuator is formed such that the outer circumference gradually increases in the flowing direction to increase the thickness. Therefore, attenuation can be performed in an extremely wide frequency range, in particular, the entire frequency range generated in a compression pulse of a screw-type compressor, that is, in the range of 250 Hz to 6,000 Hz.
However, the path of the acoustic outlet piece linearly extends from an inlet to an outlet and thus, when the flow rate becomes large to increase the inner diameter of the path, or when the whole length is made small in terms of space to decrease the distance between the inlet and the outlet, only an insufficient silencing effect may be acquired in a high frequency range. In some cases, such compact configuration having a small length cannot attenuate sound in a wide frequency range.
JP 04-105920 U discloses a silencer provided with an inlet pipe having a deep bowl-shaped extending portion, an outlet pipe having a deep bowl-shaped extending portion, and an intermediate pipe that couples the bowl-shaped extending portions of the inlet pipe to the outlet pipe.
In the silencer, a shallow bowl-shaped core body having a contracted pipe port at its concave central region is provided at the coupling site of the inlet pipe and the intermediate pipe. A core body, and a valve body including a valve portion that opens/closes the pipe port of the core body on the side of the outlet pipe are provided at the coupling site of the inlet pipe and the intermediate pipe.
However, since the silencer includes the large valve portion having a support point at the coupling site of the inlet pipe and the intermediate pipe, the valve body cannot be readily accessed at maintenance.